Efforts are currently underway in a number of groups worldwide to develop an implantable retinal prosthesis to restore at least partial sight to persons suffering from certain forms of blindness due to end-stage photoreceptor degenerative diseases such as age-related macular degeneration and hereditary retinitis pigmentosa. Such retinal prostheses, which are currently being developed, are based on the electronic transfer of visual information from a camera located in front of the eye to receiver circuitry which will be implanted within the eye to feed the visual information in pixelized form an electrode array that will be placed either in front of the retina (epiretinal) or beneath the retinal tissue (sub-retinal). Electrical currents from the electrode array will then provide artificial stimulation of neural tissue (e.g. ganglion cells) in the retina to generate the visual perception of dots of light corresponding to the pixelized visual image, with the goal of being able to restore a measure of sight to a blind person. Further details of implantable retinal prostheses to which the electrode array of the present invention can be applied can be found, for example, in U.S. Pat. Nos. 5,476,494; 5,836,996; 5,935,155; and 6,393,327 which are all incorporated herein by reference; and in an article by John Wyatt et al. entitled “Occular Implants for the Blind” published in IEEE Spectrum, pp. 47-53, May 1996; in another article by Mark S. Humayun et al. entitled “Pattern Electrical Stimulation of the Human Retina” published in Vision Research, vol. 39, pp. 2569-2576, 1999; and in yet another article by M. Schwarz et al. entitled “Single Chip CMOS Imagers and Flexible Microelectronic Stimulators for a Retinal Implant System” published in Sensors and Actuators, vol. 83, pp. 40-46, 2000.
Although progress has been made in the development of retinal prostheses, there still remains a need for an improved electrode array which can provide from hundreds to tens of thousands or more individual electrodes, each of which can conform to the curvature of the retina while providing a gentle, uniform contact pressure on the retina to prevent damage to the underlying neural cells.
The present invention represents an advance in the art by providing a micromachined electrode array which comprises, in certain embodiments, a plurality of spaced-apart electrodes, each of which is flexibly attached to a supporting substrate by a plurality of springs to allow independent movement of the individual electrodes, and to allow a spring constant of each spring to be tailored during design so that each electrode will provide substantially the same low contact force when urged into contact with the curved surface of the retina.
In other embodiments, the micromachined electrode array of the present invention can be formed with a plurality of spaced-apart electrodes which are attached to a substrate in a fixed position, and which can be independently electrically contacted, or contacted in sets.
The micromachined electrode array of the present invention can also be adapted for neural stimulation or sensing applications for many different types of neural tissue including neural tissue associated with visual, auditory and sensory systems, and for neural tissue associated with the control of muscles (e.g. for bladder function or the activation of paretic limbs).
In certain embodiments of the present invention, the electrode array can be used to sense the contact force of one or more electrodes in contact with a neural surface to ensure that the contact force does not exceed a predetermined limit, or to ensure that the contact force provided by the electrodes is substantially the same.
These and other advantages of the present invention will become evident to those skilled in the art.